Work will be continued in the following areas: A. Genetic Recombination: 1. Studies on the Structure and Mechanism of the E. coli Polynucleotide Joining Enzyme (Ligase); 2. Studies of the Role of the E. coli DNA Ligase in DNA Synthesis in vivo. B. DNA Synthesis: 1. Analysis of Terminal Nucleotide Sequences of 10S "Okazaki" Fragments; 2. DNA Polymerase I and 5' yields 3' Exonuclease Activity in DNA Polymerase 1 Mutants of E. coli.